Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.84	5.107%	$78.6621	$78.66	$78.65	$78.70
Purchase #2	$200.39	4.248%	$208.9026	$208.90	$208.90	$208.90
Purchase #3	$192.64	6.792%	$205.7241	$205.72	$205.70	$205.70
Purchase #4	$54.46	8.751%	$59.2258	$59.23	$59.25	$59.20
Purchase #5	$237.87	11.730%	$265.7722	$265.77	$265.75	$265.80
Purchase #6	$53.60	13.689%	$60.9373	$60.94	$60.95	$60.90
Purchase #7	$83.95	13.451%	$95.2421	$95.24	$95.25	$95.20
7 purchase totals =	$897.75		$974.4662	$974.46	$974.45	$974.40